Digitizers generally include a manually movable cursor and a digitizing surface or tablet. A sheet of paper or other surface bearing a two-dimensional graphic illustration or design to be converted into digital coordinates for use by a computer is laid on the digitizing surface. The cursor is then placed on the sheet of paper and manually moved from position to position to trace the illustration or design. At each desired position of the cursor, the operator customarily actuates a switch on the cursor to cause the coordinates of the position to be stored in a computer memory operatively connected to the cursor. To facilitate the alignment of the cursor with a feature of the illustration or design, the cursor is provided with cross-hairs which the operator aligns with the desired feature.
The position coordinates of a point on the digitizing surface are sensed through inductive or capacitive elements in the digitizing tablet and the cursor. Since the introduction of digitizers almost two decades ago, gradual improvements have increased the accuracy of the position sensing to a point now where accuracy limitations arise more from human error than from the crudeness of the digitizer design.